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Herbert Mayr - One of the best experts on this subject based on the ideXlab platform.
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Nucleophilicity parameters of arylsulfonyl substituted halomethyl anions
Journal of Organic Chemistry, 2017Co-Authors: Quan Chen, Peter Mayer, Herbert MayrAbstract:The rates of the reactions of the arylsulfonyl-substituted carbanions carrying α-chloro and α-bromo substituents (1a–e) with quinone methides 2a–g and benzylidenemalonates 2h and 2i in DMSO were determined photometrically at 20 °C. The reactions were performed under pseudo-first-order conditions, and the second-order rate constants were obtained as the slopes of the plots of the pseudo-first-order rate constants versus the concentrations of the reactants used in excess. The second-order rate constants correlate linearly with the parameters E of the reference electrophiles according to the linear free energy relationship log k2(20 °C) = sN(N + E), which allowed us to derive the nucleophile-specific parameters N and sN of carbanions 1a–e. The resulting Nucleophilicity parameters N (23 < N < 29) reveal the title compounds to be among the most reactive nucleophiles so far integrated on our comprehensive Nucleophilicity scale.
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the Nucleophilicity of persistent α monofluoromethide anions
Angewandte Chemie, 2016Co-Authors: Zhe Zhang, Herbert Mayr, Angel Puente, Fang Wang, Martin Rahm, Yuncai Mei, G Surya K PrakashAbstract:α-Fluorocarbanions are key intermediates in nucleophilic fluoroalkylation reactions. Although frequently discussed, the origin of the fluorine effect on the reactivity of α-fluorinated CH acids has remained largely unexplored. We have now investigated the kinetics of a series of reactions of α-substituted carbanions with reference electrophiles to elucidate the effects of α-F, α-Cl, and α-OMe substituents on the nucleophilic reactivities of carbanions.
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Nucleophilicity parameters of stabilized iodonium ylides for characterizing their synthetic potential
Journal of the American Chemical Society, 2016Co-Authors: Saloua Chelli, Konstantin Troshin, Sami Lakhdar, Armin R Ofial, Peter Mayer, Herbert MayrAbstract:Kinetics and mechanisms of the reactions of the β-dicarbonyl-substituted iodonium ylides 1(a–d) with several π-conjugated carbenium and iminium ions have been investigated. All reactions proceed with rate-determining attack of the electrophile at the nucleophilic carbon center of the ylides to give iodonium ions, which rapidly expel iodobenzene and undergo different subsequent reactions. The second-order rate constants k2 for the reactions of the iodonium ylides with benzhydrylium ions correlate linearly with the electrophilicity parameters E of the benzhydrylium ions and thus follow the linear free energy relationship log k(20 °C) = sN(N + E) (eq 1), where electrophiles are characterized by one parameter (E), while nucleophiles are characterized by two parameters: the Nucleophilicity N and the susceptibility sN. The Nucleophilicity parameters 4 < N < 8 for iodonium ylides 1(a–d) derived from these correlations show that substituting hydrogen for Ph-I+ at the carbanionic center of Meldrum’s acid or dimedo...
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Influence of the N-Substituents on the Nucleophilicity and Lewis Basicity of N-Heterocyclic Carbenes.
Organic Letters, 2016Co-Authors: Alison Levens, Herbert Mayr, Martin Breugst, David W. LuptonAbstract:The ability to modulate the Nucleophilicity and Lewis basicity of N-heterocyclic carbenes is pivotal to their application as organocatalysts. Herein we examine the impact of the N-substituent on the Nucleophilicity and Lewis basicity. Four N-substituents popular in NHC organocatalysis, namely, the N-2,6-(CH3O)2C6H3, N-Mes, N-4-CH3OC6H4, and N-tert-butyl groups, have been examined and found to strongly affect the Nucleophilicity. Thus, the N-2,6-(CH3O)2C6H3 group provides the most nucleophilic imidazolylidene NHC reported and the N-tert-butyl group one of the least. This difference in Nucleophilicity is reflected in the catalyst efficiency, as observed with a recently reported trienyl ester rearrangement.
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Nucleophilicity Parameters of Stabilized Iodonium Ylides for Characterizing Their Synthetic Potential
2016Co-Authors: Saloua Chelli, Konstantin Troshin, Sami Lakhdar, Armin R Ofial, Peter Mayer, Herbert MayrAbstract:Kinetics and mechanisms of the reactions of the β-dicarbonyl-substituted iodonium ylides 1(a–d) with several π-conjugated carbenium and iminium ions have been investigated. All reactions proceed with rate-determining attack of the electrophile at the nucleophilic carbon center of the ylides to give iodonium ions, which rapidly expel iodobenzene and undergo different subsequent reactions. The second-order rate constants k2 for the reactions of the iodonium ylides with benzhydrylium ions correlate linearly with the electrophilicity parameters E of the benzhydrylium ions and thus follow the linear free energy relationship log k(20 °C) = sN(N + E) (eq 1), where electrophiles are characterized by one parameter (E), while nucleophiles are characterized by two parameters: the Nucleophilicity N and the susceptibility sN. The Nucleophilicity parameters 4 < N < 8 for iodonium ylides 1(a–d) derived from these correlations show that substituting hydrogen for Ph-I+ at the carbanionic center of Meldrum’s acid or dimedone, respectively, reduces the Nucleophilicity by approximately 10 orders of magnitude. The iodonium ylides 1(a–d) thus have nucleophilicities similar to those of pyrroles, indoles, and silylated enol ethers and, therefore, should be suitable substrates in iminium-activated reactions. Good agreement of the measured rate constant for the cyclopropanation of the imidazolidinone-derived iminium ion 10a with the iodonium ylide 1a with the rate constant calculated by eq suggests a stepwise mechanism in which the initial nucleophilic attack of the iodonium ylide at the iminium ion is rate-determining. The reaction of cinnamaldehyde with iodonium ylide 1a catalyzed by (5S)-5-benzyl-2,2,3-trimethyl-imidazolidin-4-one (11a, MacMillan’s first-generation catalyst) gives the corresponding cyclopropane with an enantiomeric ratio of 70/30 and, thus, provides proof of principle that iodonium ylides are suitable substrates for iminium-activated cyclopropanations
Renato Contreras - One of the best experts on this subject based on the ideXlab platform.
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are electrophilicity and electrofugality related concepts a density functional theory study
Organic Letters, 2011Co-Authors: Rodrigo Ormazabaltoledo, Paola R Campodonico, Renato ContrerasAbstract:It is proposed that the electrofugality of a fragment within a molecule is determined by its group Nucleophilicity. The variation of electrofugality should be tightly related to the electron releasing ability of the substituent attached to the electrofuge moiety. This contribution closes the set of relationships between philicity and fugality quantities: while nucleofugality appears related to the group electrophilicity of the leaving group, electrofugality is related to the group Nucleophilicity of the permanent group.
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quantitative characterization of group electrophilicity and Nucleophilicity for intramolecular diels alder reactions
Organic and Biomolecular Chemistry, 2010Co-Authors: Jorge Sotodelgado, Luis R Domingo, Renato ContrerasAbstract:In a previous work (L. R. Domingo, M. J. Aurell, P. Perez and R. Contreras, Tetrahedron 2002, 58, 4417) we proposed that the difference in global electrophilicity index be taken as a measure of the polarity at the transition state in intermolecular Diels–Alder reactions. We herein extend this model to deal with intramolecular Diels–Alder (IMDA) processes. The transferability of the empirical reactivity rules established for the intermolecular DA reactions to the IMDA reactions is discussed. The analysis based on group electrophilicity and Nucleophilicity in general fails because having two different reactivity patterns within the same molecule hampers a clean classification of electrophilicity and Nucleophilicity of the interacting fragments. We introduce dual philicity indexes E1 and E2 that solve this problem by separating a series of 30 IMDA reactions into two families, namely the diene to dienophile electron flow (DDpF) and the dienophile to diene electron flow (DpDF) processes. The new indexes correctly describe the charge transfer at the transition state and the reaction mechanism expected for the title reactions.
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Nucleophilicity index from perturbed electrostatic potentials
Journal of Physical Chemistry A, 2007Co-Authors: Andres Cedillo, Renato Contreras, Juan Andres, Marcelo Galvan, Arie Aizman, V S SafontAbstract:We introduce and test a Nucleophilicity index as a new descriptor of chemical reactivity. The index is derived from a perturbation model for the interaction between the nucleophile and a positive test charge. The computational implementation of the model uses an isoelectronic process involving the minimum values of the electronic part of the perturbed molecular electrostatic potential. The working expression defining the Nucleophilicity index encompasses both the electrostatic contributions and the second-order polarization effects in a form which is consistent with the empirical scales previously proposed. The index is validated for a series of neutral nucleophiles in the gas phase for which the Nucleophilicity pattern has been experimentally established within a spectroscopic scale.
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definition of a Nucleophilicity scale
Journal of Physical Chemistry A, 2006Co-Authors: Paula Jaramillo, Patricia Perez, Renato Contreras, William Tiznado, Patricio FuentealbaAbstract:This work deals with exploring some empirical scales of Nucleophilicity. We have started evaluating the experimental indices of Nucleophilicity proposed by Legon and Millen on the basis of the measure of the force constants derived from vibrational frequencies using a probe dipole H-X (X = F,CN). The correlation among some theoretical parameters with this experimental scale has been evaluated. The theoretical parameters have been chosen as the minimum of the electrostatic potential V(min), the binding energy (BE) between the nucleophile and the H-X dipole, and the electrostatic potential measured at the position of the hydrogen atom V(H) when the complex nucleophile and dipole H-X is in the equilibrium geometry. All of them present good correlations with the experimental Nucleophilicity scale. In addition, the BEs of the nucleophiles with two other Lewis acids (one hard, BF(3), and the other soft, BH(3)) have been evaluated. The results suggest that the Legon and Millen Nucleophilicity scale and the electrostatic potential derived scales can describe in good approximation the reactivity order of the nucleophiles only when the interactions with a probe electrophile is of the hard-hard type. For a covalent interaction that is orbital controlled, a new Nucleophilicity index using information of the frontier orbitals of both, the nucleophile and the electrophile has been proposed.
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a theoretical study on the relationship between Nucleophilicity and ionization potentials in solution phase
Journal of Physical Chemistry A, 2003Co-Authors: Renato Contreras, Juan Andres, V S Safont, And P Campodonico, Jose G SantosAbstract:In this paper we describe a method to obtain estimates of the relative Nucleophilicity for a series of neutral and charged electron donors from their solution phase ionization potential (Is). The relationship between Nucleophilicity and the solution phase ionization potentials is first tested for experimental Is values in aqueous solution. On the basis of the meaningful relationship found, the method is then applied to the theoretical solution phase Is obtained at the IPCM-MP2/6-311G(2d,p) level of theory. The comparison between the experimental Nucleophilicity as given by Ritchie's N+ scale and the solution phase ionization energy for a series electron donors split out into two families: a first group of marginal and moderate nucleophiles that mainly contains atoms of the first row (H2O, NH2CONHNH2, CF3CH2NH2, NH3, CH3ONH2, NH2OH and CH3O-), with Nucleophilicity number N+ < 6.0; a second group of strong nucleophiles, mainly including second-row sulfur atom (CH3CH2S-, CH3CH2CH2S-, OHCH2CH2S-, C6H5S-) and...
Patricia Perez - One of the best experts on this subject based on the ideXlab platform.
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intrinsic relative scales of electrophilicity and Nucleophilicity
Journal of Physical Chemistry A, 2013Co-Authors: Eduardo Chamorro, Mario Duquenorena, Rafael Notario, Patricia PerezAbstract:The formulation of the second-order perturbation approach to the stabilization energy of the A–B interacting species due to charge transfer is revisited. Intrinsic (i.e., electronic) theoretical indices for both relative electrophilicity and Nucleophilicity are proposed for any electrophile (A)–nucleophile (B) pairs of combining species. By using the new descriptors, an electronic analogue to the Mayr–Patz linear free relationship has been successfully tested in the context of available experimental evidence reported for reactions of primary and secondary amines with benzhydrylium ions.
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the Nucleophilicity n index in organic chemistry
Organic and Biomolecular Chemistry, 2011Co-Authors: Luis R Domingo, Patricia PerezAbstract:The Nucleophilicity N index (J. Org. Chem.2008, 73, 4615), the inverse of the electrophilicity, , and the recently proposed inverse of the electrodonating power, , (J. Org. Chem.2010, 75, 4957) have been checked toward (i) a series of single 5-substituted indoles for which rate constants are available, (ii) a series of para-substituted phenols, and for (iii) a series of 2,5-disubstituted bicyclic[2.2.1]hepta-2,5-dienes which display concurrently electrophilic and nucleophilic behaviors. While all considered indices account well for the nucleophilic behavior of organic molecules having a single substitution, the Nucleophilicity N index works better for more complex molecules. Unlike, the inverse of the electrophilicity, , (R2 = 0.71), and the inverse of the electrodonating power, (R2 = 0.83), a very good correlation of the Nucleophilicity N index of twelve 2-substituted-6-methoxy-bicyclic[2.2.1]hepta-2,5-dienes versus the activation energy associated with the nucleophilic attack on 1,1-dicyanoethylene is found (R2 = 0.99). This comparative study allows to assert that the Nucleophilicity N index is a measure of the Nucleophilicity of complex organic molecules displaying concurrently electrophilic and nucleophilic behaviors.
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an analysis of the regioselectivity of 1 3 dipolar cycloaddition reactions of benzonitrile n oxides based on global and local electrophilicity and Nucleophilicity indices
European Journal of Organic Chemistry, 2009Co-Authors: Luis R Domingo, Eduardo Chamorro, Patricia PerezAbstract:The regioselectivity of the 1,3-dipolar cycloaddition (13DC) reactions of benzonitrile N-oxides (BNOs) with electrophilic and nucleophilic alkenes has been analyzed by using global and local Nucleophilicity and electrophilicity reactivity indices defined within the conceptual DFT. The BNOs react with electron-deficient and electron-rich ethylenes, but the regioselectivities of these polar reactions are different. Whereas the reactions with electron-rich ethylenes are completely regioselective, yielding 5-isoxazolines, a change in the regioselectivity is observed in the reactions with electron-deficient ethylenes, which yield a mixture of 4- and 5-isoxazolines. Analysis of the energies, geometries, and electronic structures of the transition-state structures involved in the 13DC reactions between the BNOs and two electronically activated ethylenes are in complete agreement with the analysis of the global and local electrophilicity and Nucleophilicity reactivity indices.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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a comparison between theoretical and experimental models of electrophilicity and Nucleophilicity
Journal of Molecular Structure-theochem, 2009Co-Authors: Eduardo Chamorro, Mario Duquenorena, Patricia PerezAbstract:Abstract Four different theoretical models of electrophilicity and Nucleophilicity has been discussed in the light of experimental available evidence for a series of 20 benzhydrylium ions taken as reference electrophilic systems and 16 primary and secondary amines as nucleophilic systems. It is shown that the theoretical scales are linearly related to the well-known experimental ones based on the electrophilicity (E) and Nucleophilicity (N and s ) parameters derived by Mayr from the rate constants k20 °C associated to general electrophile–nucleophile combinations, log k20 °C = s(N + E).
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a condensed to atom Nucleophilicity index an application to the director effects on the electrophilic aromatic substitutions
Journal of Molecular Structure-theochem, 2009Co-Authors: Patricia Perez, Luis R Domingo, Mario Duquenorena, Eduardo ChamorroAbstract:Abstract The local Nucleophilicity of simple substituted aromatic systems is shown to be described on a quantitative basis by using a condensed-to-atoms Nucleophilicity index. This quantity constitutes an extension of the global Nucleophilicity descriptor, N introduced for reagents in cycloaddition reactions and other organic molecules [Journal of Organic Chemistry 73 (2008) 4615–4624; Journal of Molecular Structure (THEOCHEM) 865 (2008) 68–72]. The local projection N k is performed on the basis of the normalization condition of the Fukui functions. It is shown that such a simple index provides useful clues about the director effects of the substituents on the electrophilic aromatic substitution (EAS) reactions of aromatic compounds. A discussion of the general frame of validity for the condensed-to-atoms model is presented.
Rainer Wilcken - One of the best experts on this subject based on the ideXlab platform.
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regioselective nitration of 3 fluoro 2 substituted benzoic acids
ChemInform, 2015Co-Authors: Konstanze Hurth, Sebastien Jacquier, Hansjoerg Lehmann, Rainer WilckenAbstract:The partially excellent regioselectivities of the nitration reaction is rationalized in most cases using Fukui indices of local Nucleophilicity.
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regioselective nitration of 3 fluoro 2 substituted benzoic acids
Tetrahedron Letters, 2015Co-Authors: Konstanze Hurth, Sebastien Jacquier, Hansjoerg Lehmann, Rainer WilckenAbstract:Abstract The preparation of a series of 3-fluoro-2-substituted-6-nitro benzoic acids is described. The partially excellent regioselectivities observed in the nitration step can be rationalized in most cases using Fukui indices of local Nucleophilicity.
Tom Welton - One of the best experts on this subject based on the ideXlab platform.
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manipulating solute Nucleophilicity with room temperature ionic liquids
Journal of the American Chemical Society, 2004Co-Authors: Lorna Crowhurst, Llewellyn N Lancaster, Juan Perez M Arlandis, Tom WeltonAbstract:In this work we report the effect of ionic liquids on a class of charge-neutral nucleophiles. We have studied the reactions of nbutylamine, di-nbutylamine, and tri-nbutylamine with methyl p-nitrobenzenesulfonate in [bmpy][N(Tf)2], [bmpy][OTf], and [bmim][OTf] (bmpy = 1-butyl-1-methylpyrrolidinium; bmim = 1-butyl-3-methylimidazolium) and compared their reactivities, k2, to those for the same reactions in the molecular solvents dichloromethane and acetonitrile. It was shown that all of the amines are more nucleophilic in the ionic liquids than in the molecular solvents studied in this work. Comparison is also made with the effect of ionic liquids on the reactivity of chloride ions, which are deactivated in ionic liquids. The Eyring activation parameters revealed that changes in the activation entropies are largely responsible for the effects seen. This can be explained in part by the differing hydrogen-bonding properties, as shown by the Kamlet−Taft solvent parameters, of each of these solvents and the form...
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Nucleophilicity in ionic liquids 3 anion effects on halide Nucleophilicity in a series of 1 butyl 3 methylimidazolium ionic liquids
Journal of Organic Chemistry, 2004Co-Authors: Llewellyn N Lancaster, Tom WeltonAbstract:We have continued the study of halide Nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF4]-, [PF6]-, [SbF6]-, [OTf]-, and [N(Tf)2]-) when the cation is [bmim]+...
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Nucleophilicity in ionic liquids 2 1 cation effects on halide Nucleophilicity in a series of bis trifluoromethylsulfonyl imide ionic liquids
Journal of Organic Chemistry, 2002Co-Authors: Llewellyn N Lancaster, Tom Welton, Paul A Salter, Brent G YoungAbstract:In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)2], [bm2im][N(Tf)2], and [bmpy][N(Tf)2] (where bmim = 1-butyl-3-methylimidazolium, bm2im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)2 = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim]+ ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters ΔH⧧, ΔS⧧, and ΔG⧧ have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.
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a study of halide Nucleophilicity in ionic liquids
Journal of The Chemical Society-perkin Transactions 1, 2001Co-Authors: Llewellyn N Lancaster, Tom Welton, Brent G YoungAbstract:The relative Nucleophilicity of chloride, bromide and iodide anions in [bmim][BF4] ionic liquid has been measured by studying their reaction with methyl p-nitrobenzenesulfonate ([bmim] = 1-butyl-3-methylimidazolium cation). It has been found that iodide is the most nucleophilic halide, and that chloride and bromide have approximately equal nucleophilicities (Cl− is slightly more nucleophilic than Br−) in [bmim][BF4]. Activation energies for the reaction of chloride and bromide with methyl p-nitrobenzenesulfonate have been calculated. The relative Nucleophilicity of the halides has been compared with that observed in molecular solvents and in a tetraalkylammonium tetraalkylboride ionic liquid.
